Use of cool·season turfgrasses in transitional environ· ments is limited, in part, by their heat tolerance. Development of a rapid heat tolerance screening technique would be of value in determining the potential of turf· grasses for use in warmer areas.The heat tolerance of 22 Kentucky bluegrass (Poa pratensis L.) cultivars, Poa annua L., and four peremliaJ ryegrass cultivars (Lolium perenne L.) was evaluated by exposing plants for 30 min to temperatures ranging from 41 to 49 C in single degree intervals. Ten-week-old plants, which had been grown under a low level of N fertilization and watered infrequently to maximize heat tolerance development, were sealed in plastic bags, placed in a con· stant temperature water bath for treatment, and then replanted. Recovery was evaluated by visually rating the plants 4 weeks after treatment or by harvesting and weighing plants 2 weeks after treatment and expressing the weight as a percentage of the weight of a nonstressed control (referred to as recovery weight). Cnltivar com· parisons were based on the average recovery weight over a given temperature range.Initial injury occurred at 41 to 43 C with complete kill at 47 to 49 C. Kentucky bluegrass was more heat tolerant than Poa annua L. and perennial ryegrass. Heat tolerance of the latter two species was approximately equal. The Kentucky bluegrass cultivars tested were similar in heat tolerance. Among the ryegrasses, 'Loretta' was less heat tolerant than 'Diplomat', 'Pennfine', and 'Citation'. Of all the grasses, 'Sydsport' Kentucky blue· grass ranked the highest and Loretta perennial ryegrass the lowest in heat tolerance. The correlation between dilute acid extractable carbohydrate reserves and recovery weight for these five cultivars was not significant. There was a significant negative correlation between recovery weight and Fe and Al concentration. Additional index words:Heat stress, Stress recovery, Carbohydrates, Mineral analyses, Poa pratensis L., Lolium perenne L., and Poa annua L. M ANAGING cool-season grasses for recreational turf in transitional areas is difficult. Heat stress often reduces turf quality when recreational facilities are receiving maximum use. In the short term, reducing N and water applications induces a "hardened" turf. The long term solution to the problem lies in identifying and incorporating heat tolerant germplasm into breeding programs. Currently available cultivars need to be screened for heat tolerance followed by studies into tolerance mechanisms.The optimum temperature for shoot growth of coolseason turfgTasses is in the range 15 to 24 C (Beard, 1973). Above 24 C, growth subsides first and then at very high temperatures, severe injury or death can occur. In controlled environment pot experiments, Kentucky bluegrass (Poa pratensis L.) produced maxi·

The goal of the professional lawn care industry is to provide the homeowner with a dark green weed-free lawn. Members of this industry are interested in techniques to enhance the color of a turfgrass stand in lieu of excessive N fertilization. The purpose ohbis research was to evaluate tbe use of foliar applications of Fe alone or in com· bination with N on the color response of Kentucky bluegrass (Poa pratensis L.). Iron sulfate or an iron chelate was applied at the rate of 1.1, 2.2, or 4.5 kg Fe ha-I in combination with either 0, 25, or 49 kg N ha-1 to a mixed 'Columbia'I'Touchdown' Kentucky bluegrass turf growing on a Catlin silt loam (fine-silty, mixed, mesic Typic Argiudoll). Color ratings and clipping weights were determined on a weekly basis until treatment effects were no longer significant. In a separate experiment, both sources of Fe were applied at rates of 1.1 to 72.4 kg Fe ha-I to Kentucky bluegrass to evaluate phytotoxicity. The color enhancement due to Fe applications without N lasted from several weeks to several months depending on the weather following application. Use of Fe during cool wet periods enhanced turf color for only 2 to 3 weeks and therefore, was considered of limited value. Iron applications during cool dry periods enhanced turf color for several months. The treatment of 2.2 kg ha-I of Fe from iron chelate was judged to be the most effective Fe treatment because the color enhancement was usually equal to that provided by a 4.5 kg rate of either source but it did not result in any discoloration as was found with the 4.5 kg rate. Combining Fe with tbe 25 kg ha-I rate of N resulted in color enhancement equal to that caused by applying 49 kg ba-I of N alone. The results of the study indicate that combining Fe with N can result in acceptable turfgrass color with lower rates of N. No permanent damage was caused to turfs receiving Fe at rates up to 72.2 kg ha-I although foliar phytotoxicity was observed.

Nitrogen applied to turfgrass stands can be lost through leaching, denitrification, or ammnnia (NH)) 'olatilization. Tbe purpose of this in,estigation was to e,aluate tbe effects of N carrier and mode of application on NH) ,olatilization from a Kentucky bluegrass (POfl prfltensis L.)turf growing on an acidic (pH 6.4) Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) soil. The NH) wbicb 'olatilized after .application of any of senral sulfur-coated ureas (SCU), prilled urea, spray-applied solubilized urea, and two liquid N products was measured by passing tbe airstream from microecosystems, in whicb tbe treated turfs were growing, througb an indicating boric acid solution to trap NH). Ammonia-N losses after sulfur-coated urea fertilization ranged from 0.2% of tbe applied N wben tbe fertilization rate was 98 kg NI ba to 2.3 % of tbe applied N wben tbe fertilization rate was 293 kg NI ba. Wben prilled urea was applied at a rate of 293 kg N/ba, NH)losses averaged 10.3% of tbe applied N wbereas 4.6 and 1.6% of tbe applied N was lost after turf was fertilized witb 49 kg NIba from spray-applied solubilized urea and prilled urea, respectively. Ammonia losses from turf treated with liquid N sources ranged from 3.2 to 4.5% of the applied N. Tbe results of tbis researcb indicate tbat ammonia volatilization occurs to a limited extent in turfgrass stands growing on an acidic soil.

Many turfgrass managers apply a portion of the total yearly N to cool‐season turfgrasses in the late fall (November). The purpose of this field study was to compare fertilization programs with and without N applications in November using both slow‐release and soluble N sources. Turfs of two different cultivars of Kentucky bluegrass (Poa pratensis L. cv. Baron and cv. Newport) growing on a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) received 10 fertilization programs utilizing urea, isobutylidene diurea (IBDU), or sulfur‐coated urea (SCU). Urea was applied four times per year with either a spring application or a late‐fall application combined with applications in early June, mid‐July, and early September (171–196 kg N ha−1 yr−1). For IBDU and SCU, application dates and N rates (kg ha−1) consisted of June 98 + September 98, June 98 + November 98, and June 49 + September 49 + November 74. The turfs were rated for color for 3 yr, and clipping weights were determined weekly for the final 2 yr of the study. Results were generally similar for both cultivars, except fewer significant differences in spring color ratings were found on Newport. An application of urea in November, without a subsequent spring fertilization, resulted in higher turf color ratings in the early spring but lower turf color ratings in May and June, compared to turf receiving a spring fertilization. Results indicate that a late‐fall application of urea may not eliminate the need for spring fertilization but may allow a reduction in the amount of N applied in spring. Turfs fertilized with SCU in November received higher color ratings in the spring than did turf fertilized with SCU in September. With IBDU, the June + September program resulted in the highest number of ratings with acceptable turf color. November IBDU applications did not result in higher color ratings in the spring and resulted in inefficient use of the N applied.

Denitrification may represent an important mechanism in the fate of N applied to turf. Denitrification losses were directly measured from fertilized 'Baron' Kentucky bluegrass (Poa pratensis L.) sod samples sealed in acrylic chambers using the acetylene inhibition technique. Losses were correlated with soil texture, percent soil sat· uration (SAT), and temperature. Losses from turf on a Hadley silt loam soil and Hadley silt soil (both coarse-silty, mixed, nonacid, mesic Typic Udifluvents) incubated at 2rC did not exceed 0.4 and 0.1 %, respectively, of the applied potassium nitrate fertilizer (4.5 g N m-2 ) when soil water levels were less than 75% saturated. Soil saturation increased denitrification losses from the silt loam and silt soils to 2.2 and 5.4% of the applied N, respectively. The relationship between percent soil saturation and denitrification loss was quadratic and highly significant for both soils. .70] existed between denitrification losses and soil temperatures between 22 and 30°C in the silt soil at 75% of soil saturation. Soil temperatures of 30°C or greater coupled with saturated soil conditions resulted in the greatest losses, equiv alent to 44.6 and 92.6% of the applied N to the silt loam and silt soils, respectively. Denitrification losses did not increase at soil tem peratures above 30°C. These results indicate that denitrification loss from fertilizers applied to turfgrasses may not be a serious problem unless the soils are saturated and at higher soil temperatures.